• Proceedings of the Korea Concrete Institute Conference
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• 1999.04a
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• pp.579-584
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• 1999

In evaluating the ultimate strength of a section for a concrete flexural member, the effect of member length is not usually considered, even though the strength tends to decrease with increase of member length. In this paper the influence of specimen length on flexural compressive strength of concrete was evaluated. For this purpose, a series of C-shaped specimens subjected to axial compression and bending moment were tested using four different length-to-depth ratios(from 1, 2, 3 and 4) of specimens with compressive strength of 58 MPa. Results indicate that the reduction in flexural compressive strength with increase of length-to-width ratios was apparent. A model equation was derived using regression analyses on the experimental data. It was also founded that the effect of specimen length on ultimate strain was negligible, but its effect of the ultimate load and the displacement at center of specimen was distinct. Finally more general model equation is also suggested.

• Journal of Korean Association for Spatial Structures
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• v.23 no.2
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• pp.69-78
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• 2023

This paper investigates the effects of aspect ratio and volume fraction of hooked-end normal-strength steel fibers on the compressive and flexural properties of high-strength concrete with specified compressive strength of 60 MPa. Three types of hooked-end steel fibers with aspect ratios of 64, 67 and 80 were considered and three volume fractions of 0.25%, 0.50% and 0.75% for each steel fiber were respectively added into each high-strength concrete mixture. The test results indicated that the addition of normal-strength steel fibers is effective to improve compressive and flexural properties of high-strength concrete but fiber aspect ratio had little effect on the modulus of elasticity and compressive strength. As steel fiber content and aspect ratio increased, flexural beahvior of notched high-strength concrete beams was effectively improved.

• Fibers and Polymers
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• v.5 no.3
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• pp.187-197
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• 2004

The compressive and flexural properties of hemp fiber reinforced concretes (FRC) were examined in this paper. Natural hemp fiber was mixed using dry and wet mixing methods to fabricate the FRC. Mechanical properties of the FRC were investigated. The main factors affecting compressive and flexural properties of the FRC materials were evaluated with an orthogonal test design. Fiber content by weight has the largest effect. The method for casting hemp FRC has been optimised. Under the optimum conditions, compressive strength increased by 4 %, flexural strength increased by 9 %, flexural toughness increased by 144 %, and flexural toughness index increased by 214 %.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2020.11a
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• pp.94-95
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• 2020

Oyster shells are characterized by coarse and coarse grains, but similar in strength to sand, and egg shells are fine grains but weak in strength. In terms of supply and demand of raw materials, oyster shells can be supplied only in limited periods and regions in winter and south coast of the year, but egg shells have the advantage of being able to supply and supply nationwide 365 days. This study aims to study the change in strength characteristics by mixing oyster shell powder and egg shell powder with the same particle size and mixing up to 150%. The conclusions of the flexural and compressive strength tests of mortar mixed with oyster shell powder and egg shell powder are as follows. The 7-day flexural and compressive strength with ESP added and the 3-day flexural and compressive strength with OSP added were similar, which is thought to be because the strength of OSP is higher than that of ESP.

• Advances in concrete construction
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• v.8 no.2
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• pp.139-144
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• 2019

In this study, the mechanical properties of reactive powder concrete (RPC) with a constant cement to silica fume ratio of 4 were investigated. In the experimental program, reactive powder concretes with steel fiber at different ratios were produced. Five productions using quartz sand with a maximum grain size of 0.6 mm were performed. A superplasticizer with a ratio of 3% of the cement was used for all productions. $40{\times}40{\times}160mm$ prismatic specimens were prepared and tested for flexural and compression. The specimens were exposed to two different curing conditions as autoclave and standard curing condition. Autoclave exposure was performed for 3 hours under a pressure of 2 MPa. It was observed that the compressive strength of concrete, along with the flexural strength exposed to autoclave was quite high compared to the strength of concretes subjected to standard curing. The results obtained indicated that the compressive strength, along with the flexural strength of autoclaved concrete increased as the amount of cement used increases. Approximately 15% increase in flexural strength was achieved with a 4% steel fiber addition. The maximum compressive strength that has been reached is over 210 MPa for reactive powder concrete for the same steel fiber ratio and with a cement content of $960kg/m^3$. The relationship between compressive strength and flexural strength of reactive powder concrete exposed to both curing conditions was also identified.

• Computers and Concrete
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• v.8 no.3
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• pp.357-369
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• 2011

In this study, effect of steel fibers on toughness and some mechanical properties of concrete were investigated. Hooked-end steel fibers were used in concrete samples with three volume fractions (${\nu}_f$) of 0.5%, 0.75% and 1% and for two aspect ratios (l/d) of 45 and 65. Compressive and flexural tensile strength and modulus of elasticity of concrete were determined for cylindrical, cubic and prismatic samples at the age of 7 and 28 days. The stress-strain curves of standard cylindrical specimens were studied to determine the effect of steel fibers on toughness of steel-fiber-reinforced concrete (SFRC). In addition, the relationship between compressive strength and the flexural tensile strength of SFRC were reported. Finally, a simple model was proposed to generate the stress-strain curves for SFRC based on strains corresponding to the peak compressive strength and 60% of peak compressive stress. The proposed model was shown to provide results in good correlation with the experimental results.

• KCI Concrete Journal
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• v.11 no.3
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• pp.89-97
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• 1999

The purpose of this research is to investigate the utilization of recycled fine aggregates as a material to apply to a building finished walls or as a decorating material in combination with a polymer. The strengths of two resin mortars using recycled fine aggregates and natural fine aggregates was made. In order to improve the workability and the strength of the resin mortar with recycled fine aggregates, partial replacement of recycled fine aggregates with natural ones was made with the application of various type of fillers. The results, it show that the compressive strength and flexural strength of resin mortar using the recycled fine aggregates were about 70% to 100% of those of resin mortar using natural fine aggregates. It was enough to assure the utilization of the recycled fine aggregates as a material for the production of resin mortar. From the result of partial replacement of recycled fine aggregates with natural ones, the compressive strength was Increased from 5% to 15% and the flexural strength was much as 5% to 20% as a result of 70% substitution It was also found that the use of garnet powder shows a similar tendency in the compressive strength and slag powder does in the flexural strength and tensile strength.

• Proceedings of the Korea Concrete Institute Conference
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• 2001.11a
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• pp.417-422
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• 2001

The purpose of this study is to investigate experimentally the workability, compressive and flexural strength properties of rapid-set concrete with various mixture. The kinds of fine aggregate(river sand, sea sand, crushed sand), water-cement ratio(40%, 45%, 50%), sand-aggrega to ratio(33%, 36%, 39%) were chosen as the experimental parameters. Test variables are temperature of concrete, slump, air contents, compressive and flexural strength. The compressive and flexural strength for 3 hours and 6 hours were tested. As result, it was shown that temperature of concrete involved 45$^{\circ}C$, some time later decreased. The workability were decreasing in steps as the sand-aggregate ratio increased and crushed sand was the highest value. Higher compressive and flexural strength was shown following the order of river sand, sea sand, crushed sand regardless of sand-aggregate ratio. But the values of gap was just a little.

• Advances in concrete construction
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• v.10 no.6
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• pp.479-488
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• 2020

The experimental and numerical works were carried out on high performance fiber reinforced concrete (HPFRC) with w/cm ratios ranging from 0.25 to 0.40, fiber volume fraction (Vf)=0-1.5% and 10% silica fume replacement. Improvements in compressive and flexural strengths obtained for HPFRC are moderate and significant, respectively, Empirical equations developed for the compressive strength and flexural strength of HPFRC as a function of fiber volume fraction. A relation between flexural strength and compressive strength of HPFRC with R=0.78 was developed. Due to the complex mix proportions and non-linear relationship between the mix proportions and properties, models with reliable predictive capabilities are not developed and also research on HPFRC was empirical. In this paper due to the inadequacy of present method, a back propagation-neural network (BP-NN) was employed to estimate the 28-day compressive strength of HPFRC mixes. BP-NN model was built to implement the highly non-linear relationship between the mix proportions and their properties. This paper describes the data sets collected, training of ANNs and comparison of the experimental results obtained for various mixtures. On statistical analyses of collected data, a multiple linear regression (MLR) model with R2=0.78 was developed for the prediction of compressive strength of HPFRC mixes, and average absolute error (AAE) obtained is 6.5%. On validation of the data sets by NNs, the error range was within 2% of the actual values. ANN model has given the significant degree of accuracy and reliability compared to the MLR model. ANN approach can be effectively used to estimate the 28-day compressive strength of fibrous concrete mixes and is practical.

• Advances in concrete construction
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• v.2 no.4
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• pp.301-308
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• 2014

The present research work is on the effect of sawdust ash (SDA) on the mechanical strengths of self compacting concrete (SCC) using naphthalene sulfonate (NS) as a plasticizer. Experiments on compressive, flexural and splitting tensile strengths are conducted and the data analyzed using the Minitab 15 software. The results showed that SDA can defer the reaction of cement hydration and prolong the setting times of cement paste. This was very much pronounced on the flexural and splitting tensile strengths at 90 days of curing which are 36 % and 33 % higher than the control strengths, respectively. The study has proposed strength relations of mortar compressive strength with the flexural and splitting tensile strengths and these are, 5 and 7 times respectively. The flexural strength is 1.5 times that of the splitting tensile. Finally, linear models were developed on these relationships.